Method of dehydrating ethanol via extractive rectification with ethylene glycol

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering, particularly to obtaining dehydrated ethanol from synthetic alcohol. The method of dehydrating ethanol via extractive rectification with ethylene glycol in one composite column, in which the composite column has a side fastening section consisting of 3 t.t, and the main column has 21 t.t, the reflux ratio in the main column and the side section is equal to (0.33-0.38) and (0.11-0.15), respectively, with extraction of ethanol in the distillate of the main column, and ethylene glycol in the still bottom, which is returned for reflux to the third plate of the main column, and water in the distillate of the side section.

EFFECT: invention enables to obtain ethanol and water of higher quality and reduce power consumption by 20,1% compared to the prototype scheme with the same ratio of the starting mixture to ethylene glycol.

1 tbl

 

The invention relates to the field of chemical technology, in particular the production of dehydrated ethanol from synthetic alcohol formed during the direct hydration of ethylene, and ethanol, obtained by enzymatic fermentation of biomass.

At a pressure of 101.3 kPa ethanol forms a water azeotropic mixture having a boiling point 78,15C and the concentration of alcohol 89,56% mol. One of the methods of separation of the mixture is extractive rectification, which is energetically more advantageous than, for example, azeotropic distillation with pentane. Known methods of implementing the dehydration of ethanol by extractive distillation with ethylene glycol (EG) in a two-column complex and in one complex column with a side selection.

The article (Meirelles, A., Weiss S. and H. Herfurth Ethanol Dehydration by Extractive Distillation, J. Chem. Tech. Biotechnol. 1992, V.53, pp.181-188) a method for dehydration of ethanol by extractive distillation with EH in a complex of two columns - column extractive distillation column and the regeneration of the glycol. In extractive column efficiency 24 theoretical plates (TT) 12 plate serves the initial mixture containing 85 mol%. ethanol and 15 mol%. water. The glycol serves on the 2nd plate. The ratio of the initial mixture:EH is 1:0,6, reflux number of 0.89. As distillate selected ethanol with a concentration of 99,94% mol. CBM about the SPS, representing a mixture of water and ethylene glycol, rectificatum in the column regeneration efficiency 10 theoretical plates. Reflux the number is 1.0. The distillate from this column is water with a concentration of 99.7 mol%, and kubovy product - glycol concentration of 99.98 mol%, which returns to irrigation in the first column.

The disadvantage of this method is the process in two columns, which requires the installation of pumps, piping and intermediate tanks for pumping a bottom liquid of the first column to the second and additional energy consumption for evaporation of the fluid in a cube column regeneration and the creation of flow phlegmy.

The closest in technical essence and the achieved result is a process of extractive distillation of a mixture of ethanol-water with ethylene glycol in the same complex column with a side selection / Brito R.R., Maciel M.R.W., Meirelles A.A. New Extractive Distillation Configuration for Separating Binary Azeotropic Mixtures. The First European Congress on Chemical Engineering. Florence, Italy. May 4-7. 1997. V.2. P.13333. /. The initial mixture with the concentration of ethanol 85 mol%. served on the 14-th plate (counting from the top), the extractive agent is on the 6th. The top product is an almost pure ethanol with a concentration of 99,71%. Water is taken in the form of a side stream in the vapor phase with 20 plates. The concentration of water in the side selection 99,27% mol. CBM flow - EG with containing the receiving impurities of 0.02 mol%. - return on irrigation in the upper part of the column. The efficiency of the column 24 TT the Ratio of the initial mixture:EH is 1:0,6, reflux number of 0.83.

The disadvantage of the prototype is not a high quality product flows and significant energy consumption in the reboiler of the column.

The technical essence of the present invention is to improve the quality of products and reduce energy consumption for the separation of a mixture of ethanol-water.

The technical problem is achieved by the process of extractive distillation in a single complex string with the side reinforcing section. The effectiveness of the main column 21 TT, the efficiency of the side sections 3 TT Reflux number in the main column (0,33-0,38); in lateral section (0,11-0,15). The initial mixture ethanol-water with a concentration of alcohol of 85 mol%. served at the boiling temperature of 13-th plate of the main column, the extractive agent at a temperature of 80C on the 3rd plate. The molar ratio of the initial mixture and ethylene glycol is 1:(of 0.47 to 0.6). The steam flow is taken into a side section with 19 plates of the main column, the flow of fluid from the side of the section return on the same plate. As distillate main column select ethanol with a total content of water and EG 0,06 mol%. VAT product of ethylene glycol with a concentration of 99.98 mol%. - return on irrigation on the 3rd plate in the main to the Onna. Water with a concentration of 99.7 mol%. taken in the form of a distillate from the side of the section.

Energy costs in the cube complex columns with lateral bracing section on the separation of an ethanol water mixture with the alcohol content of 85 mol%, calculated by computational experiment, when the ratio of the initial mixture:EH=0,6 be 64,76 MJ/KMOL power and heat load in the boiler circuit-prototype - 81,04 MJ/KMOL.

The table shows that for values reflux numbers in the main column and sidebar sections, lower than indicated in the claims, the quality of the product streams (especially water) is significantly reduced. In particular, when reflux numbers in the main column and side sections, equal to 0.28 and 0.07, respectively, the concentration of the allocated water is even lower than in the schema prototype. The increase in reflux numbers in excess of the limits specified in the claims, does not lead to significant improvements in product quality, but increases the energy consumption in the reboiler of the column.

Thus, the organization of the process in the same column with side reinforcing section allows to obtain ethanol and water of higher quality (ethanol 99,94% mol. unlike 99,71% mol. for our prototype and the water of 99.7 mol%. unlike 99,27% mol. for our prototype) and to reduce energy costs by 20.1% compared with the scheme-the prototype of the m with the same ratio of the initial mixture:EH.

The method of dehydration of ethanol by extractive distillation with ethylene glycol in the same complex column, characterized in that the complex column has side effects section consisting of 3 theoretical plates, and the main column contains 21 theoretical plate, reflux ratio in the main column and sidebar sections are 0,33-0,38 and 0.11-0.15, respectively with the selection in the main column distillate ethanol, Cuba, ethylene glycol, who return for irrigation on the 3rd plate of the main column and the distillate side sections of water.



 

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